Mechanical Technology October 2016

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26 Mechanical Technology — October 2016
⎪ Structural engineering materials, metals and non-metals ⎪
“Your bullets ricochet … I’m
bulletproof … I am ti – ta
– ni - um…”. The lyrics of
this song pop into my head
as I write this article. It seems to be my
theme song at the moment, as a lot of my
work revolves around this amazing metal.
Titanium and its alloys seem to be
a panacea for use in aggressive envi-
ronments. Properties such as a good
strength-to-weight ratio, excellent cor-
rosion resistance, higher strength and
fracture toughness than steel, high tem-
perature resistance of up to ~590 °C,
higher fatigue strength than aluminium or
magnesium alloys, low density – half that
of steels and superalloys – tick all the right
boxes for a wide range of applications.
Typical uses are in aircraft structures,
aero-engines, biomedical devices and
components in chemical processing
equipment. In 2012, 55% of titanium
metal in China was used in chemical pro-
In our Materials Engineering in Practice column this month, Leslie Chown
of the School of Chemical and Metallurgical Engineering at the University of
the Witwatersrand talks about titanium and its alloys and the dti’s aim to
create a local titanium beneficiation industry.
References
1 David Guetta lyrics from the song “Titanium”.
2 Lutjering, G and Williams, JC (2007) Titanium, 2nd Ed.
Springer.
3 ResearchinChina (2013) Global and China Titanium In-
dustry Report.
port/2013/6611.html.
4 USGS (2014) Titanium, US Geological Survey, http://minerals.
usgs.gov/minerals/pubs/commodity/titanium.
5 Wild, S. (2015) Innovation: Shaping South Africa through sci-
ence, GIBS and Macmillan.
6 Aerosud (2016):
7 Du Preez, W (2014) Beneficiation of South Africa’s titanium
resource, Presentation to the Portfolio Committee on Trade and
Industry.
8 Pickens, JR (2004), Low cost titanium for ships and tanks,
Advanced Materials and Processes, May, 37-39.
9 ONR (2012):
es/2012/Titanium-Ship-Hull-Navy-ONR.aspx.
10 ATI (2016). Armor Materials.
Pages/armor-materials.aspx.
An isolated Cu-Ni pipe and flange connected to a bronze butterfly valve
and an isolated titanium flange and pipe connection.
Photo reference: Kriedt, FA; Mountford II, JA, Scaturro, MR. (2014), Guidelines for Using
Titanium in Seawater Piping, SNAME T&R Bulletin No. 3-52, 16.
Quo vadis titanium? The status of the
titanium industry in South Africa
cessing, with about 8.0% for structural
parts in the aerospace industries and just
under 7.0 % in power generation.
Globally, South Africa has the second
largest reserves of titanium ore, and is
the largest supplier of titania slag, used
as pigments in paint, paper and plastics.
Pigments account for about 94% of titani-
um use, leaving 6.0% for metal products.
While an ingot of titanium metal can cost
$20 to 80 per kg, and high-end products
such as implants 10-1 000 times more,
slag sells for a mere $1 to $2 per kg.
So how much titanium metal from ore
does South Africa currently beneficiate?
The answer is staggering: zero tonnes per
annum. We are not capitalising on local
beneficiation of this resource, because
the Kroll process for manufacturing pure
titanium is expensive and we cannot be
competitive. However, a small but grow-
ing, local industry imports semi-finished
mill products, converting them to value-
added products such as
biomedical equipment and
large titanium aerospace
parts.
The dti aims to create a
local titanium beneficiation
industry within the next
decade. South African uni-
versities and institutes col-
laborate in the dti Titanium
Centre of Competence
(TiCoC), hosted by the CSIR.
Apart from driving com-
mercialisation of titanium
casting, powder production
and additive manufacturing
processes, this programme also ensures
that we develop human capacity around
titanium manufacture.
The ‘workhorse’ of titanium alloys
is Ti-6Al-4V. Titanium on its own is ex-
pensive, and the aluminium-vanadium
master alloy used in the production of
Ti‑6Al-4V adds to the cost. Researchers
are looking at all aspects of manufacture
to reduce the cost of titanium alloys. In
one of our research projects, the possibil-
ity of partially replacing the Al-V master
alloy with low cost ferrovanadium is being
explored. Of course, this alloy would not
compete with Ti-6Al-4V, but may offer a
cost-effective solution for an application
with less stringent requirements.
There is growing concern around life
extension, especially in power plants
and chemically aggressive industrial
environments where corrosion, high tem-
peratures, creep and wear occur. In some
cases it would be beneficial to replace
steel components entirely with suitable
titanium alloys, especially in new plants.
The initial higher cost of titanium parts is
more than offset by the savings from the
metal’s 20 to 50 year life, with reduced
equipment maintenance and down time.
The US Navy chose titanium over copper-
nickel for seawater piping systems on
LDP-17 ships, expecting titanium to last
the ship’s lifetime of 40 to 50 years, with
half of the weight. Where full replacement
of components by titanium is not viable,
coating the relevant surface may provide
a low-cost, but very effective solution.
As new technologies, such as additive
manufacturing using titanium powders
and joining titanium, are developed,
the alloys become more accessible. In
2012, the US Office of Naval Research
used friction stir welding to join plates of
titanium for a ship hull – a technology
breakthrough.
Coming back to the song – yes, tita-
nium can be bulletproof! Military-grade
products are supplied for armouring
land-based vehicles. q
Insulating
sleeve